The moderate clinical success of stem cell injections for the treatment of myocardial infarction has been mainly attributed to the low retention and survival of injected cells. Implantation of the engineered cardiac tissue patch is expected to yield improved survival of delivered cells, and potentially, a more efficient structural and functional tissue reconstruction at the infarct site. While in the past 15 years the field of cardiac tissue engineering has benefited from the use of neonatal rat cardiomyocytes, it is well recognized that these cells will remain limited to in vitro model systems and proof-of-concept in vivo studies. On the other hand, cardiac tissue patches made of stem cells offer a potential for translation to clinical practice. In particular, large quantities of cardiogenic cells can be obtained from pluripotent stem cell sources (embryonic or induced pluripotent stem cells), which offers an exciting opportunity to develop and utilize a relatively large, functional cardiac tissue patch for the treatment of myocardial injury. Unfortunately, the clear design rules to engineer a highly functional, stem cell- derived cardiac tissue patch are currently non-existent. Therefore, in order to significantly promote the field of cardiac tissue engineering, we propose to combine our novel tissue engineering approach with tools from developmental and cancer biology to design an electromechanically functional, stem cell-derived cardiac tissue patch that can rapidly vascularize and functionally integrate with host tissue and yield the repair of myocardial injury. Specifically, we propose to: 1) systematically study different mouse embryonic stem cell-derived cardiogenic populations for their ability to functionally integrate with neonatal rat myocytes and assemble into a highly functional cardiac tissue patch in vitro, 2) explore different structural and biochemical factors to enhance vascularization, survival, and functionality of these tissue patches upon implantation in mouse dorsal skin flap chamber model, and 3) investigate implantation conditions in the setting of mouse myocardial infarction to yield safe and efficient functional integration of the patch and host tissue, and consequently, a significantly improved cardiac function. The knowledge obtained in this project will allow us to pursue in the future engineering of a functional cardiac tissue patch made of human stem cells for potential clinical applications.